Genetic and environmental contributions to alcohol dependence risk in a national twin sample: consistency of findings in women and men

Haplotype-based study of the association of alcohol and acetaldehyde-metabolising genes with alcohol dependence (with or without comorbid anxiety symptoms) in a Cape Mixed Ancestry population

Alcohol dependence (AD) has a large heritable component. Genetic variation in genes involved in the absorption and elimination of ethanol have been associated with AD. However, some of these polymorphisms are not present in an African population. Previous studies have reported that a type of AD which is characterized by anxious behaviour may be a genetically specific subtype of AD. We investigated whether variation in genes encoding cytochrome P450 2E1 (CYP2E1) or acetaldehyde-metabolising enzymes (ALDH1A1, ALDH2) might alter the risk of AD, with and without symptoms of anxiety, in a Cape population with mixed ancestry. Eighty case control pairs (one with AD, one without AD) were recruited and individually matched for potential confounders. Genotype data were available for 29 single-nucleotide polymorphisms (SNPs) across the three genes. Linkage disequilibrium D' values were evaluated for all pairwise comparisons. Allele and haplotype frequencies were compared between cases and controls using a χ2 test. The ACAG haplotype in block 4 of the ALDH1A1 gene provided evidence of an association with AD (p = 0.03) and weak evidence of an association with AD without symptoms of anxiety (p = 0.06). When a genetic score was constructed using SNPs showing nominal evidence of association with AD, every extra risk allele increased the odds of AD by 35% (OR 1.35, 95% CI 1.08, 1.68, p = 0.008) and the odds of having AD with anxiety symptoms increased by 53% (OR 1.53, 95% CI 1.14, 2.05, p = 0.004). Although our results are supported by previous studies in other populations, they must be interpreted with caution due to the small sample size and the potential influence of population stratification.

Association between copy number variation losses and alcohol dependence across African American and European American ethnic groups

BACKGROUND

Copy number variations (CNVs) are structural genetic mutations consisting of segmental gains or losses in DNA sequence. Although CNVs contribute substantially to genomic variation, few genetic and imaging studies report association of CNVs with alcohol dependence (AD). Our purpose is to find evidence of this association across ethnic populations and genders. This work is the first AD-CNV study across ethnic groups and the first to include the African American (AA) population.

METHODS

This study considers 2 CNV data sets, one for discovery (2,345 samples) and the other for validation (239 samples), both including subjects with AD and healthy controls of European and African ancestry. Our analysis assesses the association between AD and CNV losses across ethnic groups and gender by examining the effect of overall losses across the whole genome, collective losses within individual cytogenetic bands, and specific losses in CNV regions.

RESULTS

Results from the discovery data set showed an association between CNV losses within 16q12.2 and AD diagnosis (p = 4.53 × 10(-3) ). An overlapping CNV region from the validation data set exhibited the same direction of effect with respect to AD (p = 0.051). This CNV region affects the genes CES1p1 and CES1, which are members of the carboxylesterase (CES) family. The enzyme encoded by CES1 is a major liver enzyme that typically catalyzes the decomposition of ester into alcohol and carboxylic acid and is involved in drug or xenobiotics, fatty acid, and cholesterol metabolisms. In addition, the most significantly associated CNV region was located at 9p21.2 (p = 1.9 × 10(-3) ) in our discovery data set. Although not observed in the validation data set, probably due to small sample size, this result might hold potential connection to AD given its connection with neuronal death. In contrast, we did not find any association between AD and the overall total losses or the collective losses within individual cytogenetic bands.

CONCLUSIONS

Overall, our study provides evidence that the specific CNVs at 16q12.2 contribute to the development of alcoholism in AA and European American populations.

Motherhood, Psychological Risks, and Resources in Relation to Alcohol Use Disorder: Are There Differences between Black and White Women?

Rates of alcohol use disorders (AUD) are generally low among women who have ever had children (mothers) compared to women who have never had children (nonmothers), presenting a motherhood advantage. It is unclear if this advantage accrues to “Black” and “White” women alike. Using National Epidemiological Survey on Alcohol and Related Conditions (NESARC) wave 2 cross-sectional data that is rich in alcohol use and psychological measures, we examined the following: (a) if motherhood is protective for past-year AUD among Black (N = 4,133) and White women (N = 11,017); (b) potential explanatory psychological mechanisms; and (c) the role of race. Prevalence of a past-year DSM-IV AUD was lower among White mothers compared to White nonmothers, but this same advantage was not observed for Black women. Perceived stress was a risk for all women, but race-ethnic segregated social networks and perceived discrimination predicted current AUD for Black mothers. Unlike White mothers, current psychological factors but not family history of alcohol problems predicted AUD for Black mothers. Future prospective studies should address the mechanisms by which race, motherhood, and psychological factors interactively affect AUD in women.

Polygenic scores predict alcohol problems in an independent sample and show moderation by the environment

Alcohol problems represent a classic example of a complex behavioral outcome that is likely influenced by many genes of small effect. A polygenic approach, which examines aggregate measured genetic effects, can have predictive power in cases where individual genes or genetic variants do not. In the current study, we first tested whether polygenic risk for alcohol problems-derived from genome-wide association estimates of an alcohol problems factor score from the age 18 assessment of the Avon Longitudinal Study of Parents and Children (ALSPAC; n = 4304 individuals of European descent; 57% female)-predicted alcohol problems earlier in development (age 14) in an independent sample (FinnTwin12; n = 1162; 53% female). We then tested whether environmental factors (parental knowledge and peer deviance) moderated polygenic risk to predict alcohol problems in the FinnTwin12 sample. We found evidence for both polygenic association and for additive polygene-environment interaction. Higher polygenic scores predicted a greater number of alcohol problems (range of Pearson partial correlations 0.07-0.08, all p-values ≤ 0.01). Moreover, genetic influences were significantly more pronounced under conditions of low parental knowledge or high peer deviance (unstandardized regression coefficients (b), p-values (p), and percent of variance (R2) accounted for by interaction terms: b = 1.54, p = 0.02, R2 = 0.33%; b = 0.94, p = 0.04, R2 = 0.30%, respectively). Supplementary set-based analyses indicated that the individual top single nucleotide polymorphisms (SNPs) contributing to the polygenic scores were not individually enriched for gene-environment interaction. Although the magnitude of the observed effects are small, this study illustrates the usefulness of polygenic approaches for understanding the pathways by which measured genetic predispositions come together with environmental factors to predict complex behavioral outcomes.

Polymorphisms in genes encoding dopamine signalling pathway and risk of alcohol dependence: a systematic review

BACKGROUND

Alcohol dependence (AD) is one of the major elements that significantly influence drinking pattern that provoke the alcohol-induced organ damage. The structural and neurophysiologic abnormalities in the frontal lobes of chronic alcoholics were revealed by magnetic resonance imaging scans. It is well known that candidate genes involved in dopaminergic pathway are of immense interest to the researchers engaged in a wide range of addictive disorders. Dopaminergic pathway gene polymorphisms are being extensively studied with respect to addictive and behavioral disorders.

METHODS

From the broad literature available, the current review summarizes the specific polymorphisms of dopaminergic genes that play a role in alcohol dependence.

RESULTS

No evidence indicating any strong association between AD and polymorphisms of dopamine pathway genes has emerged from the literature.

DISCUSSION

Further studies are warranted, considering a range of alcohol-related traits to determine the genes that influence alcohol dependence.

Examination of genetic variation in GABRA2 with conduct disorder and alcohol abuse and dependence in a longitudinal study

Previous studies have shown associations between single nucleotide polymorphisms (SNPs) in gamma aminobutyric acid receptor alpha 2 (GABRA2) and adolescent conduct disorder (CD) and alcohol dependence in adulthood, but not adolescent alcohol dependence. The present study was intended as a replication and extension of this work, focusing on adolescent CD, adolescent alcohol abuse and dependence (AAD), and adult AAD. Family based association tests were run using Hispanics and non-Hispanic European American subjects from two independent longitudinal samples. Although the analysis provided nominal support for an association with rs9291283 and AAD in adulthood and CD in adolescence, the current study failed to replicate previous associations between two well replicated GABRA2 SNPs and CD and alcohol dependence. Overall, these results emphasize the utility of including an independent replication sample in the study design, so that the results from an individual sample can be weighted in the context of its reproducibility.

A twin study of alcohol dependence, binge eating, and compensatory behaviors

OBJECTIVE

Rates of alcohol dependence are elevated in women with eating disorders who engage in binge eating or compensatory behaviors compared with women with eating disorders who do not report binge eating or compensatory behaviors and with healthy controls. Alcohol dependence, binge eating, and compensatory behaviors are heritable; however, it is unclear whether a shared genetic liability contributes to the phenotypic association among these traits, and little information exists regarding this shared liability in men. We investigated genetic and environmental correlations among alcohol dependence, binge eating, and compensatory behaviors in male and female twins.

METHOD

Participants included 5,993 same- and opposite-sex twins from the Australian Twin Registry who completed a modified version of the Semi-Structured Assessment for the Genetics of Alcoholism that assessed lifetime alcohol dependence and binge eating as defined in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised. Compensatory behaviors were assessed via a general health questionnaire in women only. Biometrical twin models estimated genetic and environmental influences on alcohol dependence, binge eating, and compensatory behaviors.

RESULTS

In women, the multivariate twin model suggested that additive genetic and nonshared environmental effects influenced alcohol dependence, binge eating, and compensatory behaviors, with heritability estimates ranging from 38% to 53%. The best-fitting sex-limitation model was a common effects model that equated all genetic and nonshared environmental influences in men and women. The heritability estimates were 50% and 38% for alcohol dependence and binge eating, respectively. Overall, there were significant genetic correlations between alcohol dependence and binge eating, alcohol dependence and compensatory behaviors, and binge eating and compensatory behaviors.

CONCLUSIONS

These findings indicate that common genetic factors may underlie the vulnerability to alcohol dependence and the liability to binge eating and compensatory behaviors.

Alcohol dependence and reproductive timing in African and European ancestry women: findings in a midwestern twin cohort

OBJECTIVE

We examined associations between reproductive onset and history of alcohol dependence (AD) in 475 African ancestry (AA) and 2,865 European or other ancestry (EA) female twins.

METHOD

Participants were drawn from a U.S. midwestern birth cohort study of like-sex female twin pairs born between 1975 and 1985, ages 21-32 as of last completed assessment. Cox proportional hazards regression models were estimated predicting age at first childbirth from history of AD, separately by race/ethnicity, without and with adjustment for sociodemographic characteristics, body mass index, history of other substance involvement, psychopathology, and family and childhood risks.

RESULTS

Among EA twins, AD predicted early childbearing through age 17 and delayed childbearing from age 25 onward; in adjusted models, AD was associated with overall delayed childbearing. Among AA twins, reproductive timing and AD were not significantly related in either unadjusted or adjusted models.

CONCLUSIONS

Findings for twins of European ancestry are consistent with well-documented links between early alcohol mis/use and teenage parenting as well as delays in childbearing associated with drinking-related reproductive and relationship difficulties. Extension of analyses to other racial/ethnic groups of sufficient sample size remains important.

Genetic and environmental factors underlying comorbid bulimic behaviours and alcohol use disorders: a moderating role for the dysregulated personality cluster?

Women with bulimia nervosa (BN) frequently have co-occurring alcohol use disorders (AUDs). Studies of shared genetic transmission of these disorders have been mixed. Personality heterogeneity among individuals with BN may explain discrepant findings. Cluster analysis has characterized women with BN in groups on the basis of personality profiles. One group, the Dysregulated cluster, characterized largely by behavioural disinhibition and emotional dysregulation may be more closely linked etiologically to AUDs. This study examined whether genetic associations between BN and AUDs are the strongest among the Dysregulated cluster. Symptoms of BN and AUDs were assessed in female twins at ages 17 and 25 years from the Minnesota Twin Family Study. Personality clusters were defined using the Multidimensional Personality Questionnaire. Twin moderation models suggested small-to-moderate common genetic transmission between BN and AUDs. However, shared genetic effects did not differ by personality cluster. Findings suggest that personality clusters are unlikely to account for inconsistent findings regarding their shared aetiology.

Family-based association analysis of alcohol dependence criteria and severity

BACKGROUND

Despite the high heritability of alcohol dependence (AD), the genes found to be associated with it account for only a small proportion of its total variability. The goal of this study was to identify and analyze phenotypes based on homogeneous classes of individuals to increase the power to detect genetic risk factors contributing to the risk of AD.

METHODS

The 7 individual DSM-IV criteria for AD were analyzed using latent class analysis (LCA) to identify classes defined by the pattern of endorsement of the criteria. A genome-wide association study was performed in 118 extended European American families (n = 2,322 individuals) densely affected with AD to identify genes associated with AD, with each of the 7 DSM-IV criteria, and with the probability of belonging to 2 of 3 latent classes.

RESULTS

Heritability for DSM-IV AD was 61% and ranged from 17 to 60% for the other phenotypes. A single nucleotide polymorphism (SNP) in the olfactory receptor OR51L1 was significantly associated (7.3 × 10(-8) ) with the DSM-IV criterion of persistent desire to, or inability to, cut down on drinking. LCA revealed a 3-class model: the "low-risk" class (50%) rarely endorsed any criteria and none met criteria for AD; the "moderate-risk" class (33%) endorsed primarily 4 DSM-IV criteria and 48% met criteria for AD; and the "high-risk" class (17%) manifested high endorsement probabilities for most criteria and nearly all (99%) met criteria for AD. One SNP in a sodium leak channel NALCN demonstrated genome-wide significance with the high-risk class (p = 4.1 × 10(-8) ). Analyses in an independent sample did not replicate these associations.

CONCLUSIONS

We explored the genetic contribution to several phenotypes derived from the DSM-IV AD criteria. The strongest evidence of association was with SNPs in NALCN and OR51L1.

Genetic and environmental influences on the ages of drinking and gambling initiation: evidence for distinct aetiologies and sex differences

AIMS

To investigate the genetic and environmental contributions to age at first drink (AFD) and age first gambled (AFG), assess their overlap and examine sex differences.

DESIGN

Univariate twin models were fitted to decompose the variation in AFD and AFG into additive genetic, shared environmental and unique environmental factors. Bivariate genetic models were fitted to assess the genetic and environmental contributions to the sources of covariation in AFD and AFG.

SETTING

National Australian Twin Registry.

PARTICIPANTS

A total of 4542 same-sex and opposite-sex twins aged 32-43 years, 42% male and 58% female.

MEASUREMENTS

AFD and AFG were assessed via structured psychiatric telephone interviews. Age of onset was treated as both continuous and categorical (early/late onset).

FINDINGS

AFD and AFG were modestly correlated (r = 0.18). Unique environmental influences explained a substantial proportion of the variation in both AFD (0.55, 95% confidence interval [CI] = 0.50-0.61) and AFG (0.66, 95% CI = 0.59-0.72), but these influences were uncorrelated (rE  = 0.01). Additive genetic factors explained a notable proportion of variation in AFG (0.21, 95% CI = 0.003-0.39), while shared environmental factors were important for AFD (0.31, 95% CI = 0.15-0.46). Among men, genetic factors influenced variation in AFG but not in AFD and shared environmental factors influenced variation in AFD but not in AFG. Among women, shared environmental factors influenced variation in both AFD and AFG, but these environmental factors were not significantly correlated (rC  = 0.09).

CONCLUSIONS

Among Australian twins, age at first drink and age first gambled are influenced by distinct unique environmental factors, and the genetic and environmental underpinnings of both phenotypes differ in men and women.

Association of the CHRNA4 neuronal nicotinic receptor subunit gene with frequency of binge drinking in young adults

Background

Binge drinking is responsible for over half of all alcohol‐related deaths and results in significant health and economic costs to individuals and society. Knowledge of genetic aspects of this behavior, particularly as it emerges in young adulthood, could lead to improved treatment and prevention programs.

Methods

We have focused on the association of variation in neuronal nicotinic receptor subunit genes (CHRNs) in a cohort of 702 Hispanic and non‐Hispanic White young adults who are part of the Social and Emotional Contexts of Adolescent Smoking Patterns (SECASP) study. Fifty‐five single nucleotide polymorphisms (SNPs) covering the variation in 5 CHRNs (CHRNA4,CHRNB2,CHRNA2, CHRNB3A6, and CHRNA5A3B4) were studied.

Results

Frequency of binge drinking and other correlated alcohol consumption measures were significantly associated with SNPs in CHRNA4 (p‐values ranged from 0.0003 to 0.02), but not with SNPs in other CHRNs. This association was independent of smoking status in our cohort.

Conclusions

Variants in CHRNA4 may contribute to risk of binge drinking in young adults in this cohort. Results will need to be confirmed in independent samples.

Moderators of the association between peer and target adolescent substance use

Associating with substance using peers is generally considered as one of the most important predictors of adolescent substance use. However, peer association does not affect all adolescents in the same way. To better understand when and under what conditions peer association is most linked with adolescent substance use (SU), this review focuses on the factors that may operate as moderators of this association. The review highlighted several potential moderators reflecting adolescents' individual characteristics (e.g., pubertal status, genes and personality), peer and parental factors (e.g., nature of relationships and parental monitoring), and contextual factors (e.g., peer, school and neighborhood context). As peer association is a broad concept, important methodological aspects were also addressed in order to illustrate how they can potentially bias interpretation. Taking these into account, we suggest that, while the effects of some moderators are clear (e.g., parental monitoring and sensation seeking), others are less straightforward (e.g., neighborhood) and need to be further examined. This review also provides recommendations for addressing different methodological concerns in the study of moderators, including: the use of longitudinal and experimental studies and the use of mediated moderation. These will be key for developing theory and effective prevention.

Parental separation and early substance involvement: results from children of alcoholic and cannabis dependent twins

BACKGROUND

Risks associated with parental separation have received limited attention in research on children of parents with substance use disorders. We examined early substance involvement as a function of parental separation during childhood and parental alcohol and cannabis dependence.

METHOD

Data were drawn from 1318 adolescent offspring of monozygotic (MZ) or dizygotic (DZ) Australian twin parents. Cox proportional hazards regression analyses were conducted predicting age at first use of alcohol, first alcohol intoxication, first use and first regular use of cigarettes, and first use of cannabis, from parental separation and both parent and cotwin substance dependence. Parent and cotwin alcohol and cannabis dependence were initially modeled separately, with post hoc tests for equality of effects.

RESULTS

With few exceptions, risks associated with parental alcohol versus cannabis dependence could be equated, with results largely suggestive of genetic transmission of risk from parental substance (alcohol or cannabis) dependence broadly defined. Controlling for parental substance dependence, parental separation was a strong predictor for all substance use variables, especially through age 13.

CONCLUSION

Together, findings underscore the importance of parental separation as a risk-factor for early substance involvement over and above both genetic and environmental influences specific to parental alcohol and cannabis dependence.

Understanding alcohol use disorders with neuroelectrophysiology

Neurocognitive deficits associated with impairments in various brain regions and neural circuitries, particularly involving frontal lobes, have been associated with chronic alcoholism, as well as with a predisposition to develop alcohol use and related disorders (AUDs). AUD is a multifactorial disorder caused by complex interactions between behavioral, genetic, and environmental liabilities. Neuroelectrophysiologic techniques are instrumental in understanding brain and behavior relationships and have also proved very useful in evaluating the genetic diathesis of alcoholism. This chapter describes findings from neuroelectrophysiologic measures (electroencephalogram, event-related potentials, and event-related oscillations) related to acute and chronic effects of alcohol on the brain and those that reflect underlying deficits related to a predisposition to develop AUDs and related disorders. The utility of these measures as effective endophenotypes to identify and understand genes associated with brain electrophysiology, cognitive networks, and AUDs has also been discussed.

Integrating GWASs and human protein interaction networks identifies a gene subnetwork underlying alcohol dependence

Despite a significant genetic contribution to alcohol dependence (AD), few AD-risk genes have been identified to date. In the current study, we aimed to integrate genome-wide association studies (GWASs) and human protein interaction networks to investigate whether a subnetwork of genes whose protein products interact with one another might collectively contribute to AD. By using two discovery GWAS data sets of the Study of Addiction: Genetics and Environment (SAGE) and the Collaborative Study on the Genetics of Alcoholism (COGA), we identified a subnetwork of 39 genes that not only was enriched for genes associated with AD, but also collectively associated with AD in both European Americans (p < 0.0001) and African Americans (p = 0.0008). We replicated the association of the gene subnetwork with AD in three independent samples, including two samples of European descent (p = 0.001 and p = 0.006) and one sample of African descent (p = 0.0069). To evaluate whether the significant associations are likely to be false-positive findings and to ascertain their specificity, we examined the same gene subnetwork in three other human complex disorders (bipolar disorder, major depressive disorder, and type 2 diabetes) and found no significant associations. Functional enrichment analysis revealed that the gene subnetwork was enriched for genes involved in cation transport, synaptic transmission, and transmission of nerve impulses, all of which are biologically meaningful processes that may underlie the risk for AD. In conclusion, we identified a gene subnetwork underlying AD that is biologically meaningful and highly reproducible, providing important clues for future research into AD etiology and treatment.

Association of functional DBH genetic variants with alcohol dependence risk and related depression and suicide attempt phenotypes: results from a large multicenter association study

OBJECTIVE

Dopamine-beta-hydroxylase (DBH) metabolizes the conversion of dopamine to noradrenaline. DBH, located on chromosome 9q34.2 has variants with potential functional consequences which may be related to alterations of neurotransmitter function and several psychiatric phenotypes, including alcohol dependence (AD), depression (MD) and suicidal behavior (SA). The aim of this association study in a large multicenter sample of alcohol-dependent individuals and controls is to investigate the role of DBH SNPs and haplotypes in AD risk and associated phenotypes (AD with MD or SA).

METHOD

1606 inpatient subjects with DSM-IV AD from four addiction treatment centers and 1866 control subjects were included. Characteristics of AD, MD and SA were obtained using standardized structured interviews. After subjects were genotyped for 4 DBH polymorphisms, single SNP case-control and haplotype analyses were conducted.

RESULTS

rs1611115 (near 5') C-allele and related haplotypes were significantly associated with alcohol dependence in females. This association with female alcohol dependence also accounts for the significant relationship between this variant and comorbid conditions and traits.

CONCLUSIONS

This study presents evidence for a potentially functional DBH variant influencing the risk for alcohol dependence while other comorbid conditions are not independently influenced by this SNP. However, the study also supports the possible role of the dopamine system in the etiology of female alcohol dependence.

A genome-wide association study of alcohol-dependence symptom counts in extended pedigrees identifies C15orf53

Several studies have identified genes associated with alcohol-use disorders (AUDs), but the variation in each of these genes explains only a small portion of the genetic vulnerability. The goal of the present study was to perform a genome-wide association study (GWAS) in extended families from the Collaborative Study on the Genetics of Alcoholism to identify novel genes affecting risk for alcohol dependence (AD). To maximize the power of the extended family design, we used a quantitative endophenotype, measured in all individuals: number of alcohol-dependence symptoms endorsed (symptom count (SC)). Secondary analyses were performed to determine if the single nucleotide polymorphisms (SNPs) associated with SC were also associated with the dichotomous phenotype, DSM-IV AD. This family-based GWAS identified SNPs in C15orf53 that are strongly associated with DSM-IV alcohol-dependence symptom counts (P=4.5 × 10(-8), inflation-corrected P=9.4 × 10(-7)). Results with DSM-IV AD in the regions of interest support our findings with SC, although the associations were less significant. Attempted replications of the most promising association results were conducted in two independent samples: nonoverlapping subjects from the Study of Addiction: Genes and Environment (SAGE) and the Australian Twin Family Study of AUDs (OZALC). Nominal association of C15orf53 with SC was observed in SAGE. The variant that showed strongest association with SC, rs12912251 and its highly correlated variants (D'=1, r(2) 0.95), have previously been associated with risk for bipolar disorder.

Stress-response pathways are altered in the hippocampus of chronic alcoholics

The chronic high-level alcohol consumption seen in alcoholism leads to dramatic effects on the hippocampus, including decreased white matter, loss of oligodendrocytes and other glial cells, and inhibition of neurogenesis. Examining gene expression in post mortem hippocampal tissue from 20 alcoholics and 19 controls allowed us to detect differentially expressed genes that may play a role in the risk for alcoholism or whose expression is modified by chronic consumption of alcohol. We identified 639 named genes whose expression significantly differed between alcoholics and controls at a False Discovery Rate (FDR) ≤ 0.20; 52% of these genes differed by at least 1.2-fold. Differentially expressed genes included the glucocorticoid receptor and the related gene FK506 binding protein 5 (FKBP5), UDP glycosyltransferase 8 (UGT8), urea transporter (SLC14A1), zinc transporter (SLC39A10), Interleukin 1 receptor type 1 (IL1R1), thioredoxin interacting protein (TXNIP), and many metallothioneins. Pathways related to inflammation, hypoxia, and stress showed activation, and pathways that play roles in neurogenesis and myelination showed decreases. The cortisol pathway dysregulation and increased inflammation identified here are seen in other stress-related conditions such as depression and post-traumatic stress disorder and most likely play a role in addiction. Many of the detrimental effects on the hippocampus appear to be mediated through NF-κB signaling. Twenty-four of the differentially regulated genes were previously identified by genome-wide association studies of alcohol use disorders; this raises the potential interest of genes not normally associated with alcoholism, such as suppression of tumorigenicity 18 (ST18), BCL2-associated athanogene 3 (BAG3), and von Willebrand factor (VWF).

Determining the heritability of ethanol-induced locomotor sensitization in mice using short-term behavioral selection

RATIONALE

Sensitization to the locomotor stimulant effects of alcohol (ethanol) is thought to be a heritable risk factor for the development of alcoholism that reflects progressive increases in the positive motivational effects of this substance. However, very little is known about the degree to which genes influence this complex behavioral phenomenon.

OBJECTIVES

The primary goal of this work was to determine the heritability of ethanol-induced locomotor sensitization in mice using short-term behavioral selection.

METHODS

Genetically heterogeneous C57BL/6J (B6) × DBA/2J (D2) F2 mice were generated from B6D2F1 progenitors, phenotyped for the expression of locomotor sensitization, and bred for high (HLS) and low (LLS) expression of this behavior. Selective breeding was conducted in two independently generated replicate sets to increase the confidence of our heritability estimates and for future correlated trait analyses.

RESULTS

Large and significant differences in locomotor sensitization between HLS and LLS lines were evident by the fourth generation. Twenty-two percent of the observed line difference(s) were attributable to genes (h² = .22). Interestingly, locomotor activity in the absence of ethanol was genetically correlated with ethanol sensitization; high activity was associated with high sensitization.

CONCLUSIONS

That changes in ethanol sensitivity following repeated exposures are genetically regulated highlights the relevance of studies aimed at determining how genes regulate susceptibility to ethanol-induced behavioral and neural adaptations. As alcohol use and abuse disorders develop following many repeated alcohol exposures, these data emphasize the need for future studies determining the genetic basis by which changes in response to alcohol occur.

Genetic and environmental influences on alcohol use problems: moderation by romantic partner support, but not family or friend support

BACKGROUND

High levels of various forms of social support (e.g., romantic partner, family, friend) have a buffering effect on alcohol use outcomes in both adolescents and adults. The etiological associations among these variables have not been well studied. One possibility is that social support may buffer against inherited genetic predispositions to alcohol problems. Previous work has examined gene-environment interactions (G×E) for alcohol use disorders, but never for social support in adult twins.

METHODS

In the current study, biometric modeling techniques were implemented to examine genetic and environmental components of variance of social support and alcohol use problems in a sample of 672 adult twin pairs. Using biometric moderation models that estimate G×E in the presence of gene-environment correlation (rGE), analyses examined how genetic and environmental influences on alcohol use problems varied as a function of romantic partner support, family support, and friend support.

RESULTS

Genetic and environmental components of variance for alcohol use problems varied depending on the level of romantic partner support, with greater environmental influences found at the low level of support. Family and friend support, however, failed to show moderating effects.

CONCLUSIONS

The current research has implications for expanding our understanding of what types of social support may trigger or suppress genetic and environmental influences on alcohol use problems.

Genetic and environmental influences on the familial transmission of externalizing disorders in adoptive and twin offspring

IMPORTANCE

Twin-family studies have shown that parent-child resemblance on substance use disorders and antisocial behavior can be accounted for by the transmission of a general liability to a spectrum of externalizing disorders. Most studies, however, include only biological parents and offspring, which confound genetic and environmental transmission effects.

OBJECTIVE

To examine the familial transmission of externalizing disorders among both adoptive (genetically unrelated) and biological relatives to better distinguish genetic and environmental mechanisms of transmission.

DESIGN

Family study design wherein each family included the mother, father, and 2 offspring, including monozygotic twin, dizygotic twin, nontwin biological, and adoptive offspring. Structural equation modeling was used to estimate familial transmission effects and their genetic and environmental influences.

SETTING

Participants were recruited from the community and assessed at a university laboratory.

PARTICIPANTS

A total of 1590 families with biological offspring and 409 families with adoptive offspring. Offspring participants were young adults (mean age, 26.2 years).

MAIN OUTCOMES AND MEASURES

Symptom counts of conduct disorder, adult antisocial behavior, and alcohol, nicotine, and drug dependence. RESULTS There was a medium effect for the transmission of the general externalizing liability for biological parents (r = 0.27-0.30) but not for adoptive parents (r = 0.03-0.07). In contrast, adoptive siblings exhibited significant similarity on the general externalizing liability (r = 0.21). Biometric analyses revealed that the general externalizing liability was highly heritable (a2 = 0.61) but also exhibited significant shared environmental influences (c2 = 0.20).

CONCLUSIONS AND RELEVANCE

Parent-child resemblance for substance use disorders and antisocial behavior is primarily due to the genetic transmission of a general liability to a spectrum of externalizing disorders. Including adoptive siblings revealed a greater role of shared environmental influences on the general externalizing liability than previously detected in twin studies and indicates that sibling rather than parent-child similarity indexes important environmental risk factors for externalizing disorders.

A behavioral-genetic investigation of bulimia nervosa and its relationship with alcohol use disorder

Bulimia nervosa (BN) and alcohol use disorder (AUD) frequently co-occur and may share genetic factors; however, the nature of their association is not fully understood. We assessed the extent to which the same genetic and environmental factors contribute to liability to BN and AUD. A bivariate structural equation model using a Cholesky decomposition was fit to data from 7241 women who participated in the Swedish Twin study of Adults: Genes and Environment. The proportion of variance accounted for by genetic and environmental factors for BN and AUD and the genetic and environmental correlations between these disorders were estimated. In the best-fitting model, the heritability estimates were 0.55 (95% CI: 0.37; 0.70) for BN and 0.62 (95% CI: 0.54; 0.70) for AUD. Unique environmental factors accounted for the remainder of variance for BN. The genetic correlation between BN and AUD was 0.23 (95% CI: 0.01; 0.44), and the correlation between the unique environmental factors for the two disorders was 0.35 (95% CI: 0.08; 0.61), suggesting moderate overlap in these factors. The findings from this investigation provide additional support that some of the same genetic factors may influence liability to both BN and AUD.

Rare SERINC2 variants are specific for alcohol dependence in individuals of European descent

OBJECTIVES

We have previously reported a top-ranked risk gene [i.e., serine incorporator 2 gene (SERINC2)] for alcohol dependence in individuals of European descent by analyzing the common variants in a genome-wide association study. In the present study, we comprehensively examined the rare variants [minor allele frequency (MAF)<0.05] in the NKAIN1-SERINC2 region to confirm our previous finding.

MATERIALS AND METHODS

A discovery sample (1409 European-American patients with alcohol dependence and 1518 European-American controls) and a replication sample (6438 European-Australian family participants with 1645 alcohol-dependent probands) were subjected to an association analysis. A total of 39,903 individuals from 19 other cohorts with 11 different neuropsychiatric and neurological disorders served as contrast groups. The entire NKAIN1-SERINC2 region was imputed in all cohorts using the same reference panels of genotypes that included rare variants from the whole-genome sequencing data. We stringently cleaned the phenotype and genotype data, and obtained a total of about 220 single-nucleotide polymorphisms in individuals of European descent and about 450 single-nucleotide polymorphisms in the individuals of African descent with 0

RESULTS

Using a weighted regression analysis implemented in the program SCORE-Seq, we found a rare variant constellation across the entire NKAIN1-SERINC2 region that was associated with alcohol dependence in European-Americans (Fp: overall, P=1.8×10(-4); VT: overall, P=1.4×10(-4); Collapsing, P=6.5×10(-5)) and European-Australians (Fp: overall, P=0.028; Collapsing, P=0.025), but not in African-Americans, and not associated with any other disorder examined. Association signals in this region came mainly from SERINC2, a gene that codes for an activity-regulated protein expressed in the brain that incorporates serine into lipids. In addition, 26 individual rare variants were nominally associated with alcohol dependence in European-Americans (P<0.05). The associations of five of these rare variants that lay within SERINC2 showed region-wide significance (P<α=0.0006) and 25 associations survived correction for a false discovery rate (q<0.05). The associations of two rare variants at SERINC2 were replicated in European-Australians (P<0.05).

CONCLUSION

We concluded that SERINC2 was a replicable and significant risk gene specific for alcohol dependence in individuals of European descent.

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Key Words

• serinc2
• alcohol dependence
• rare variant constellations
• european descent
• association

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MESH Headings

• Black or African American/genetics
• Alcoholism/complications
• Alcoholism/genetics
• Australia
• Case-Control Studies
• Genetic Association Studies
• Genetic Variation
• Genome-Wide Association Study
• Humans
• Membrane Proteins/genetics
• Mental Disorders/genetics
• Nervous System Diseases/genetics
• Polymorphism, Single Nucleotide
• Regression Analysis
• Risk Factors
• White People/genetics

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Grants

• R01 DA016750 NIDA NIH HHS
• R01NS45012 NINDS NIH HHS
• R01MH62873 NIMH NIH HHS
• R01MH59566 NIMH NIH HHS
• R01 MH059587 NIMH NIH HHS
• R01 MH059586 NIMH NIH HHS
• U01 HG004436 NHGRI NIH HHS
• R01 MH061675 NIMH NIH HHS
• U01HG004446 NHGRI NIH HHS
• U01MH79470 NIMH NIH HHS
• U01HG004438 NHGRI NIH HHS
• R01 MH062873 NIMH NIH HHS
• R01 NS045012 NINDS NIH HHS
• U01MH79469 NIMH NIH HHS
• U01 HG004438 NHGRI NIH HHS
• R01MH59588 NIMH NIH HHS
• U10AA008401 NIAAA NIH HHS
• U01 HG004446 NHGRI NIH HHS
• K01 DA029643 NIDA NIH HHS
• G0601030 Medical Research Council
• R01MH81800 NIMH NIH HHS
• R01MH61675 NIMH NIH HHS
• 075491/Z/04 Wellcome Trust
• R01MH59571 NIMH NIH HHS
• U01 MH046276 NIMH NIH HHS
• P60 AA011998 NIAAA NIH HHS
• R01MH59586 NIMH NIH HHS
• P01 CA089392 NCI NIH HHS
• R21 AA021380 NIAAA NIH HHS
• U01 MH079469 NIMH NIH HHS
• R01MH60870 NIMH NIH HHS
• R01MH059160 NIMH NIH HHS
• R01 MH081803 NIMH NIH HHS
• R01 MH067257 NIMH NIH HHS
• U01HG004422 NHGRI NIH HHS
• P60AA011998 NIAAA NIH HHS
• R01 MH060870 NIMH NIH HHS
• R01 MH081800 NIMH NIH HHS
• R01DA013423 NIDA NIH HHS
• R01MH081803 NIMH NIH HHS
• R01 MH059571 NIMH NIH HHS
• R01 MH059565 NIMH NIH HHS
• R01MH67257 NIMH NIH HHS
• R01DA016750 NIDA NIH HHS
• U01 HG004422 NHGRI NIH HHS
• R01MH60879 NIMH NIH HHS
• R01 DA013423 NIDA NIH HHS
• R01MH59587 NIMH NIH HHS
• U01 MH079470 NIMH NIH HHS
• HHSN268200782096C NHLBI NIH HHS
• U01 MH046289 NIMH NIH HHS
• U01HG004436 NHGRI NIH HHS
• R01 MH059566 NIMH NIH HHS
• R21 AA020319 NIAAA NIH HHS
• Wellcome Trust
• U10 AA008401 NIAAA NIH HHS
• R01AA013320 NIAAA NIH HHS
• R01 MH059588 NIMH NIH HHS
• U01 MH046318 NIMH NIH HHS
• R01MH59565 NIMH NIH HHS
• U01MH46282 NIMH NIH HHS
• M01RR165001 NCRR NIH HHS
• R01 MH060879 NIMH NIH HHS
• R01 AA013320 NIAAA NIH HHS
• R01 AA016015 NIAAA NIH HHS

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Affiliation(s)

Lingjun Zuo Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
Ke-Sheng Wang Department of Biostatistics and Epidemiology, College of Public Health, East Tennessee State University, Johnson City, TN, USA
Xiang-Yang Zhang Menninger Department of Psychiatry and Behavioral Sciences, Baylor College of Medicine, Houston, Texas, USA
Chiang-Shan R. Li Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
Fengyu Zhang Lieber Institute for Brain Development, Johns Hopkins University Medical Campus, Baltimore, MD, USA
Xiaoping Wang Department of Neurology, First People's Hospital, Shanghai Jiaotong University, Shanghai, China
Wenan Chen Department of Biostatistics, Virginia Commonwealth University, Richmond, VA, USA
Guimin Gao Department of Biostatistics, Virginia Commonwealth University, Richmond, VA, USA
Heping Zhang Department of Biostatistics, Yale University School of Epidemiology and Public Health, New Haven, CT, USA
John H. Krystal Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA Psychiatry Services, Yale-New Haven Hospital, New Haven, CT VA Alcohol Research Center, VA Connecticut Healthcare System, West Haven, CT
Xingguang Luo Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA

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Genetics and alcoholism

Alcohol is widely consumed; however, excessive use creates serious physical, psychological and social problems and contributes to the pathogenesis of many diseases. Alcohol use disorders (that is, alcohol dependence and alcohol abuse) are maladaptive patterns of excessive drinking that lead to serious problems. Abundant evidence indicates that alcohol dependence (alcoholism) is a complex genetic disease, with variations in a large number of genes affecting a person's risk of alcoholism. Some of these genes have been identified, including two genes involved in the metabolism of alcohol (ADH1B and ALDH2) that have the strongest known affects on the risk of alcoholism. Studies continue to reveal other genes in which variants affect the risk of alcoholism or related traits, including GABRA2, CHRM2, KCNJ6 and AUTS2. As more variants are analysed and studies are combined for meta-analysis to achieve increased sample sizes, an improved picture of the many genes and pathways that affect the risk of alcoholism will be possible.

A genetic perspective on the proposed inclusion of cannabis withdrawal in DSM-5

BACKGROUND

Various studies support the inclusion of cannabis withdrawal in the diagnosis of cannabis use disorder (CUD) in the upcoming DSM-5. The aims of the current study were to (1) estimate the prevalence of DSM-5 cannabis withdrawal (criterion B), (2) estimate the role of genetic and environmental influences on individual differences in cannabis withdrawal and (3) determine the extent to which genetic and environmental influences on cannabis withdrawal overlap with those on DSM-IV-defined abuse/dependence.

METHOD

The sample included 2276 lifetime cannabis-using adult Australian twins. Cannabis withdrawal was defined in accordance with criterion B of the proposed DSM-5 revisions. Cannabis abuse/dependence was defined as endorsing one or more DSM-IV criteria of abuse or three or more dependence criteria. The classical twin model was used to estimate the genetic and environmental influences on variation in cannabis withdrawal, along with its covariation with abuse/dependence.

RESULTS

Of all the cannabis users, 11.9% met criteria for cannabis withdrawal. Around 50% of between-individual variation in withdrawal could be attributed to additive genetic variation, and the rest of the variation was mostly due to non-shared environmental influences. Importantly, the genetic influences on cannabis withdrawal almost completely (99%) overlapped with those on abuse/dependence.

CONCLUSIONS

We have shown that cannabis withdrawal symptoms exist among cannabis users, and that cannabis withdrawal is moderately heritable. Genetic influences on cannabis withdrawal are the same as those affecting abuse/dependence. These results add to the wealth of literature that recommends the addition of cannabis withdrawal to the diagnosis of DSM-5 CUD.

Does personality affect risk for dementia? A systematic review and meta-analysis

OBJECTIVE

A life course epidemiologic approach suggests that personality may have lifelong pathways of influence on risk of dementia and mild cognitive impairment (MCI). This article aimed to systematically review case-control and prospective studies on the association between personality and risk of these cognitive disorders.

METHODS

Studies were identified through Scopus, Medline, PubMed, and PsycINFO. Searches combined terms for personality with those for dementia and MCI. Data were extracted and checked by a second reviewer, systematically reviewed, and meta-analyzed where appropriate.

RESULTS

Twelve longitudinal and three case-control studies were included. Five of nine studies found that higher neuroticism was associated with greater dementia risk (pooled hazard ratio [HR] per unit increase on neuroticism score, HR = 1.13, 95% confidence interval [CI] = 1.08-1.18, z = 5.11, p <0.001, N = 3,285), and two studies showed it increased risk of MCI. Three of four studies showed that higher conscientiousness was protective against dementia (pooled HR = 0.88, 95% CI = 0.81-0.97, z = 3.34, p = 0.001, N = 1,687), and one of two studies suggested it reduced risk of MCI. Three of four studies found no association between openness and dementia; however, pooled data suggested openness was protective (HR = 0.88, 95% CI = 0.81-0.97, z = 2.34, p = 0.008, N = 1,687). Seven studies indicated that extraversion was not linked with dementia, and four found no association between agreeableness and dementia.

CONCLUSIONS

Neuroticism increased risk for dementia, and conscientiousness reduced risk. The protective effect of openness was tentative. Extraversion and agreeableness were not associated with dementia. Personality should be incorporated in conceptual models of dementia risk. Clinicians and public health professionals should consider personality when planning dementia risk reduction strategies.

Dimensions of parental alcohol use/problems and offspring temperament, externalizing behaviors, and alcohol use/problems

BACKGROUND

Alcohol consumption (AC) and alcohol problems (AP) are complex traits. How many factors reflecting parental AC and AP are present in the large prospectively followed Avon Longitudinal Study of Parents and Children cohort? Would these factors be uniquely associated with various temperamental and alcohol-related outcomes in the children?

METHODS

We factor-analyzed multiple items reflecting maternal and paternal AC and AP measured over a 12-year period from before the birth of the child (n = 14,093 families). We examined, by linear regression controlling for socioeconomic status, the relationship between scales derived from these factors and offspring early childhood temperament, externalizing traits, and adolescent AC and AP (ns ranging from 9,732 to 3,454).

RESULTS

We identified 5 coherent factors: typical maternal AC, maternal AC during pregnancy, maternal AP, paternal AC, and paternal AP. In univariate analyses, maternal and paternal AC and AP were modestly and significantly associated with low shyness, sociability, hyperactivity, and conduct problems in childhood and early adolescence; delinquent behavior at age 15; and AC and AP at ages 15 and 18. AC and AP at age 18 were more strongly predicted by parental factors than at age 15. Maternal AC during pregnancy uniquely predicted externalizing traits at ages 4, 13, and 15.

CONCLUSIONS

Parental AC and AP are complex multidimensional traits that differ in their association with a range of relevant measures in their children. Controlling for background AC and AP, self-reported levels of maternal AC during pregnancy uniquely predicted externalizing behaviors in childhood and adolescence.

Association between DPYSL2 gene polymorphisms and alcohol dependence in Caucasian samples

The DPYSL2 gene at 8p22-p21 is expressed widely in neuronal tissues and has been implicated in multiple psychiatric disorders such as Alzheimer's disease and schizophrenia. We therefore hypothesized that DPYSL2 gene polymorphisms may play a role in alcohol dependence (AD). We investigated the genetic associations of 57 single-nucleotide polymorphisms (SNPs) within the DPYSL2 gene with AD using two Caucasian samples-the Collaborative Study on the Genetics of Alcoholism (COGA) sample (660 AD cases and 400 controls), and the Study of Addiction: Genetics and Environment (SAGE) sample (623 cases and 1,016 controls). The SNP rs11995227 was most significantly associated with AD (p = 0.000122) in the COGA sample while one flanking SNP rs7832576 revealed the second most significant association with AD (p = 0.00163) in the COGA sample and association with AD (p = 0.0195) in the SAGE sample. Meta-analysis of two samples showed both rs119952227 and rs7832576 were associated with AD (p = 0.000363 and 0.000184, respectively). Furthermore, the C-A haplotype from rs11995227 and rs7832576 revealed significant association with AD (p = 0.0000899) in the COGA sample while the T-G haplotype revealed association with AD both in the COGA and SAGE samples (p = 0.00098 and 0.021, respectively). These findings suggest that genetic variants in DPYSL2 may play a role in susceptibility to AD.

Common biological networks underlie genetic risk for alcoholism in African- and European-American populations

Alcohol dependence (AD) is a heritable substance addiction with adverse physical and psychological consequences, representing a major health and economic burden on societies worldwide. Genes thus far implicated via linkage, candidate gene and genome-wide association studies (GWAS) account for only a small fraction of its overall risk, with effects varying across ethnic groups. Here we investigate the genetic architecture of alcoholism and report on the extent to which common, genome-wide SNPs collectively account for risk of AD in two US populations, African-Americans (AAs) and European-Americans (EAs). Analyzing GWAS data for two independent case-control sample sets, we compute polymarker scores that are significantly associated with alcoholism (P = 1.64 × 10(-3) and 2.08 × 10(-4) for EAs and AAs, respectively), reflecting the small individual effects of thousands of variants derived from patterns of allelic architecture that are population specific. Simulations show that disease models based on rare and uncommon causal variants (MAF < 0.05) best fit the observed distribution of polymarker signals. When scoring bins were annotated for gene location and examined for constituent biological networks, gene enrichment is observed for several cellular processes and functions in both EA and AA populations, transcending their underlying allelic differences. Our results reveal key insights into the complex etiology of AD, raising the possibility of an important role for rare and uncommon variants, and identify polygenic mechanisms that encompass a spectrum of disease liability, with some, such as chloride transporters and glycine metabolism genes, displaying subtle, modifying effects that are likely to escape detection in most GWAS designs.

Are there differences between young African-American and European-American women in the relative influences of genetics versus environment on age at first drink and problem alcohol use?

BACKGROUND

Differences in age at initiation of alcohol use and rates of problem drinking between African Americans and European Americans are well documented, but the association between early and problem use-and distinctions by ethnic group in this association-have yet to be examined in a genetically informative framework.

METHODS

Data were derived from a longitudinal study of female twins in Missouri. The sample was composed of 3,532 twins (13.6% African-American [AA], 86.4% European-American [EA]), who participated in the fourth wave of data collection and reported consumption of at least 1 alcoholic drink over the lifetime. Mean age at Wave 4 was 21.7 (range = 18 to 29) years. Twin modeling was conducted to estimate the relative contributions of additive genetic (A), shared environmental (C), and unique environmental (E) factors to variation in age at first drink and problem alcohol use and the cross-phenotype overlap in these influences.

RESULTS

Early initiation of alcohol use predicted problem use in EA but not AA women. Separate AA and EA twin models produced substantially different estimates (but not statistically different models) of the relative contributions of A and C to problem alcohol use but similar genetic correlations between the phenotypes. Whereas 33% of the variance in the EA model of problem use was attributed to C, no evidence for C was found in the AA model. Heritability estimates for problem alcohol use were 41% in the AA model, 21% in the EA model. Evidence for A and C were found in both AA and EA models of age at first drink, but the A estimate was higher in the EA than AA model (44% vs. 26%).

CONCLUSIONS

Findings are suggestive of distinctions between AA versus EA women in the relative contribution of genetic and environmental influences on the development of problem drinking.

Gender differences in lifetime alcohol dependence: results from the national epidemiologic survey on alcohol and related conditions

BACKGROUND

An extensive clinical literature has noted gender differences in the etiology and clinical characteristics of individuals with alcohol dependence (AD). Despite this knowledge, many important questions remain.

METHODS

Using the 2001 to 2002 National Epidemiologic Survey on Alcohol and Related Conditions (n = 43,093), we examined differences in sociodemographic characteristics, psychiatric and medical comorbidities, clinical correlates, risk factors, and treatment-utilization patterns of men (N = 2,974) and women (N = 1,807) with lifetime AD.

RESULTS

Men with lifetime AD were more likely than women to be diagnosed with any substance use disorder and antisocial personality disorder, whereas women were more likely to have mood and anxiety disorders. After adjusting for sociodemographic characteristics and gender differences in psychiatric comorbidity in the general population, AD was associated with externalizing disorders and any mood disorder among women only. Men with AD met more criteria, had longer episodes, and were younger at the age of first drink. There were no gender differences in remission rates. Women with AD were more likely to have a family and a spouse with history of alcohol use disorders. Treatment rates were low for both genders, and women were more likely to report social stigmatization as a treatment barrier.

CONCLUSIONS

There are important gender differences in the psychiatric comorbidities, risk factors, clinical characteristics, and treatment-utilization patterns among individuals with lifetime AD.

Decision making in the pathway from genes to psychiatric and substance use disorders

In influencing risk for psychiatric and substance use disorders, genes are typically conceptualized as working in silent physiological pathways in the bowels of our biology, far from the influences of human desires. I here argue that this model of gene action is too restricted. At the individual, family and societal level, humans can, through their decision-making capacity, intervene in causal pathways from genes to behavior. At the individual level, I present four paradigmatic cases involving alcohol dependence, major depression, general externalizing behaviors and animal phobia showing how human decisions can inhibit the expression of risk genes. I review the literatures demonstrating that parental behaviors can suppress or augment the heritability of traits in their children, and social attitudes can alter and even create causal pathways from genes to phenotypes. We evolved from organisms whose nervous systems were networks of reflexes that then developed simple cognitive systems and finally self-reflection. Just as our cognitions have gone 'meta,' we are now nearing a time when we can go 'meta' about our genetic risk. For many psychiatric disorders, our risk genes are not entirely cordoned off in our silent, purposeless biological substrate. Rather, we are able to make decisions that impact on the expression of our own genomes, those of our loved ones and those of our friends and neighbors. Our actions and our genes are often weaved together, integrated into the fabric of our lives.

μ-Opioid receptor gene (OPRM1) polymorphism A118G: lack of association in Finnish populations with alcohol dependence or alcohol consumption

Aims: The molecular epidemiological studies on the association of the opioid receptor µ-1 (OPRM1) polymorphism A118G (Asn40Asp, rs1799971) and alcohol use disorders have given conflicting results. The aim of this study was to test the possible association of A118G polymorphism and alcohol use disorders and alcohol consumption in three large cohort-based study samples. Methods: The association between the OPRM1 A118G (Asn40Asp, rs1799971) polymorphism and alcohol use disorders and alcohol consumption was analyzed using three different population-based samples: (a) a Finnish cohort study, Health 2000, with 503 participants having a DSM-IV diagnosis for alcohol dependence and/or alcohol abuse and 506 age- and sex-matched controls; (b) a Finnish cohort study, FINRISK (n = 2360) and (c) the Helsinki Birth Cohort Study (n = 1384). The latter two populations lacked diagnosis-based phenotypes, but included detailed information on alcohol consumption. Results: We found no statistically significant differences in genotypic or allelic distribution between controls and subjects with alcohol dependence or abuse diagnoses. Likewise no significant effects were observed between the A118G genotype and alcohol consumption. Conclusion: These results suggest that A118G (Asn40Asp) polymorphism may not have a major effect on the development of alcohol use disorders at least in the Finnish population.

Effect of homozygous deletions at 22q13.1 on alcohol dependence severity and cue-elicited BOLD response in the precuneus

Copy number variations (CNVs) can alter the DNA sequence in blocks ranging from kilobases to megabases, involving more total nucleotides than single nucleotide polymorphisms. Yet, its impact in humans is far from fully understood. In this study, we investigate the relationship of genome-wide CNVs with brain function elicited by an alcohol cue in 300 participants with alcohol use disorders. First, we extracted refined neurobiological phenotypes, the brain responses to an alcohol cue versus a juice cue in the precuneus, thalamus and anterior cingulate cortex (ACC). Then, we correlated the CNVs with incidence frequency > 1% to the neurobiological phenotypes. One CNV region at 22q13.1 was identified to be associated with alcohol dependence severity and the brain response to alcohol cues. Specifically, the 22k base-pair homozygous deletion at 22q13.1 affects genes APOBEC3a and APOBEC3b. Carriers of this homozygous deletion show a significantly higher score in the alcohol dependence severity (P < 0.05) and increased response to alcohol cues in the precuneus (P < 10(-12) ) than other participants. Tests of a mediation model indicate that the precuneus mediates the association between the homozygous deletions and alcohol dependence severity. Interestingly, the precuneus is not only anatomically and functionally connected to the ACC and thalamus (the main active regions to the alcohol cue), but also has the most predictive power to the alcohol dependence severity. These findings suggest that the homozygous deletion at 22q13.1 may have an important impact on the function of the precuneus with downstream implications for alcohol dependence.

NKAIN1-SERINC2 is a functional, replicable and genome-wide significant risk gene region specific for alcohol dependence in subjects of European descent

OBJECTIVE

We aimed to identify novel, functional, replicable and genome-wide significant risk regions specific for alcohol dependence using genome-wide association studies (GWASs).

METHODS

A discovery sample (1409 European-American cases with alcohol dependence and 1518 European-American controls) and a replication sample (6438 European-Australian family subjects with 1645 alcohol dependent probands) underwent association analysis. Nineteen other cohorts with 11 different neuropsychiatric disorders served as contrast groups. Additional eight samples underwent expression quantitative locus (eQTL) analysis.

RESULTS

A genome-wide significant risk gene region (NKAIN1-SERINC2) was identified in a meta-analysis of the discovery and replication samples. This region was enriched with 74 risk SNPs (unimputed); half of them had significant cis-acting regulatory effects. The distributions of -log(p) values for the SNP-disease associations or SNP-expression associations in this region were consistent throughout eight independent samples. Furthermore, imputing across the NKAIN1-SERINC2 region, we found that among all 795 SNPs in the discovery sample, 471 SNPs were nominally associated with alcohol dependence (1.7×10(-7)≤p≤0.047); 53 survived region- and cohort-wide correction for multiple testing; 92 SNPs were replicated in the replication sample (0.002≤p≤0.050). This region was neither significantly associated with alcohol dependence in African-Americans, nor with other non-alcoholism diseases. Finally, transcript expression of genes in NKAIN1-SERINC2 was significantly (p<3.4×10(-7)) associated with expression of numerous genes in the neurotransmitter systems or metabolic pathways previously associated with alcohol dependence.

CONCLUSION

NKAIN1-SERINC2 may harbor a causal variant(s) for alcohol dependence. It may contribute to the disease risk by way of neurotransmitter systems or metabolic pathways.

Aberrant histone deacetylase2-mediated histone modifications and synaptic plasticity in the amygdala predisposes to anxiety and alcoholism

BACKGROUND

Epigenetic mechanisms have been implicated in psychiatric disorders, including alcohol dependence. However, the epigenetic basis and role of specific histone deacetylase (HDAC) isoforms in the genetic predisposition to anxiety and alcoholism is unknown.

METHODS

We measured amygdaloid HDAC activity, levels of HDAC isoforms, and histone H3 acetylation in selectively bred alcohol-preferring (P) and -nonpreferring (NP) rats. We employed HDAC2 small interfering RNA infusion into the central nucleus of amygdala (CeA) of P rats to determine the causal role of HDAC2 in anxiety-like and alcohol-drinking behaviors. Chromatin immunoprecipitation analysis was performed to examine the histone acetylation status of brain-derived neurotrophic factor (Bdnf) and activity-regulated cytoskeleton associated protein (Arc) genes. Golgi-Cox staining was performed to measure dendritic spine density.

RESULTS

We found that P rats innately display higher nuclear HDAC activity and HDAC2 but not HDAC 1, 3, 4, 5, and 6 protein levels and lower acetylation of H3-K9 but not H3-K14, in the CeA and medial nucleus of amygdala compared with NP rats. Acute ethanol exposure decreased amygdaloid HDAC activity and HDAC2 protein levels, increased global and gene (Bdnf and Arc)-specific histone acetylation, and attenuated anxiety-like behaviors in P rats but had no effects in NP rats. The HDAC2 knockdown in the CeA attenuated anxiety-like behaviors and voluntary alcohol but not sucrose consumption in P rats and increased histone acetylation of Bdnf and Arc with a resultant increase in protein levels that correlated with increased dendritic spine density.

CONCLUSIONS

These novel data demonstrate the role of HDAC2-mediated epigenetic mechanisms in anxiety and alcoholism.

Association of VMAT2 gene polymorphisms with alcohol dependence

Alcohol-related diseases cause significant harm in the western world. Up to 65 % of the phenotypic variance is genetically determined. Few candidate genes have been identified, comprising ADH4, ALDH2, COMT, CRHR1, DAT (SLC6A3), GABRA2 and MAOA. While abnormalities in the dopaminergic mesolimbic reward system are considered important mediators of alcoholism, studies analyzing variants of dopamine receptors showed conflicting results. Other modulators of the reward system are synaptosomal genes. Among candidate genes, polygenic variants of the Vesicular Monamine Transporter 2 (VMAT2) gene locus associated with alterations of drinking behavior were published. These variants comprise single nucleotide polymorphisms (SNPs) within the promoter region and the open reading frame. In this study, we confirm the association of VMAT2 SNP rs363387 (allelic association: p = 0.015) with alcohol dependence. This SNP defines several haplotypes including up to four SNPs (minimal p = 0.0045). In addition, numeric effects in the subgroups of males and patients with positive family history were found. We suggest that several rs363387 T-allele containing haplotypes increase the risk of alcohol dependence (OR 1.53), whereas G-allele containing haplotypes confer protection against alcohol dependence. Taken together, there is supporting evidence for a contribution of VMAT2 gene variants to phenotypes of alcohol dependence.

Genome-wide DNA methylation patterns in discordant sib pairs with alcohol dependence

INTRODUCTION

Alcohol dependence is a complex disease caused by a confluence of environmental and genetic factors. Epigenetic mechanisms have been shown to play an important role in the pathogenesis of alcohol dependence.

METHODS

To determine if alterations in gene-specific methylation were associated with alcohol dependence, a genome-wide DNA methylation analysis was performed on peripheral blood mononuclear cells from alcohol-dependent patients and siblings without alcohol dependence as controls. The Illumina Infinium Human Methylation450 BeadChip was used and gene-specific methylation of DNA isolated from peripheral blood mononuclear cells was assessed. Genes ALDH1L2, GAD1, DBH and GABRP were selected to validate beadchip results by pyrosequencing.

RESULTS

Compared to normal controls, 865 hypomethylated and 716 hypermethylated CG sites in peripheral blood mononuclear cell DNA in alcohol-dependent patients were identified. The most hypomethylated CG site is located in the promoter of SSTR4 (somatostatin receptor 4) and the most hypermethylated CG site is GABRP (gamma-aminobutyric acid A receptor). The results from beadchip analysis were consistent with that of pyrosequencing.

DISCUSSION

DNA methylation might be associated with alcohol dependence. Genes SSTR4, ALDH1L2, GAD1, DBH and GABRP may participate in the biological process of alcohol dependence.

Genetic and environmental influences on the relationship between mastery and alcohol dependence

BACKGROUND

Sense of mastery, a personal resource, is likely to have an inverse association with alcohol dependence. Previous evidence, however, is sparse. In addition, the extent to which an association is due to genetic or environmental factors is unknown.

METHODS

Data were from 3,983 male twins and 2,630 female twins who had ever used alcohol, interviewed in the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. Mastery was measured by a 6-item scale. Lifetime diagnosis of alcohol dependence was based on DSM-IV criteria assessed in a structured diagnostic interview. Univariate analyses modeled the relative contributions of genetic and environmental factors to mastery and alcohol dependence using Mx software. Bivariate Cholesky models were fit to the mastery and alcohol dependence raw data.

RESULTS

In the best-fitting model of mastery, genetic factors accounted for about 33% of the observed variance. Nonshared environmental factors, including random measurement error, accounted for the remaining 67%. Fifty-six percent of the variance in liability to alcohol dependence was genetic, and the other 44% was explained by the nonshared environment. The phenotypic polychoric correlation between mastery and alcohol dependence of -0.18 was primarily (67% in the best-fitting model) explained by genes common to both low mastery and alcohol dependence; the rest was explained by nonshared environmental factors.

CONCLUSIONS

The findings indicate that genetic risk for alcohol dependence overlaps with genetic factors that influence sense of mastery. Key challenges for future research are to identify the genes that influence mastery and alcohol dependence, as well as the environmental pathways by which they come to be linked.

Genetics of alcohol dependence and social work research: do they mix?

Since completion of the mapping of the human genome in early 2000, tremendous progress has been made in the identification of many different genes associated with our health and across diseases. Although social work researchers are not expected to conduct genetic research at the molecular level, it is imperative that we are able to understand the basic genetic findings related to behavioral problems and are able to translate and integrate this information into psychosocial treatment approaches and program development. This article is an introduction and overview of genetic approaches, using studies of the genetics of alcoholism to exemplify important issues. The literature review is not comprehensive and focuses primarily on the Collaborative Study on the Genetics of Alcoholism project as an example of a multidisciplinary and integrative approach to the genetic study of a major health problem often encountered in social work practice.

Family-based association analysis of alcohol dependence implicates KIAA0040 on Chromosome 1q in multiplex alcohol dependence families

Background

A previous genome-wide linkage study of alcohol dependence in multiplex families found a suggestive linkage result for a region on Chromosome 1 near microsatellite markers D1S196 and D1S2878. The KIAA0040 gene has been mapped to this region (1q24 - q25). A recent genome-wide association study using SAGE (the Study of Addiction: Genetics and Environment) and COGA (Collaborative Study on the Genetics of Alcoholism) found five SNPs within the KIAA0040 gene significantly associated with alcohol dependence. A meta-analysis using data from these sources also found the KIAA0040 gene significantly associated with alcohol dependence.

Methods

Using family data consisting of 1000 individuals with phenotypic data (762 with both phenotype and DNA), finer mapping of a 0.3 cM region that included the KIAA0040 gene and a flanking gene was undertaken using SNPs with minor allele frequency (MAF) ≥ 0.15 and pair-wise linkage disequilibrium (LD) of r² < 0.8 using the HapMap CEU population.

Results

Significant FBAT p-values were observed for six SNPs, four within the KIAA0040 gene (rs2269650, rs2861158, rs1008459, rs2272785) and two adjacent to KIAA0040 (rs10912899 and rs3753555). Five haplotype blocks of varying size were identified using HAPLOVIEW. Analysis using the haplotype-based test function of FBAT revealed one two-SNP block (rs1008459-rs2272785) associated with alcohol dependence. This block showed a pattern of transmission in which one haplotype, CT, with a frequency of 0.577 was found to be over-transmitted to affected offspring (p = 0.017) while another haplotype, AG, with a frequency of 0.238 was found to be under-transmitted to affected offspring (p = 0.006). A three-SNP block (rs1008459-rs2272785-rs375355) showed an overall significant association (p = 0.011) with alcohol dependence with the haplotype ACT over-transmitted to affected offspring (p = 0.016) and the haplotype GAG under-transmitted (p = 0.002).

Conclusions

Family-based association analysis shows the KIAA0040 gene significantly associated with alcohol dependence. The potential importance of the KIAA0040 gene for AD risk is currently unknown. However, the present results support earlier findings from a genome-wide association study.

Neuronal nicotinic acetylcholine receptors: common molecular substrates of nicotine and alcohol dependence

Alcohol and nicotine are often co-abused. As many as 80-95% of alcoholics are also smokers, suggesting that ethanol and nicotine, the primary addictive component of tobacco smoke, may functionally interact in the central nervous system and/or share a common mechanism of action. While nicotine initiates dependence by binding to and activating neuronal nicotinic acetylcholine receptors (nAChRs), ligand-gated cation channels normally activated by endogenous acetylcholine (ACh), ethanol is much less specific with the ability to modulate multiple gene products including those encoding voltage-gated ion channels, and excitatory/inhibitory neurotransmitter receptors. However, emerging data indicate that ethanol interacts with nAChRs, both directly and indirectly, in the mesocorticolimbic dopaminergic (DAergic) reward circuitry to affect brain reward systems. Like nicotine, ethanol activates DAergic neurons of the ventral tegmental area (VTA) which project to the nucleus accumbens (NAc). Blockade of VTA nAChRs reduces ethanol-mediated activation of DAergic neurons, NAc DA release, consumption, and operant responding for ethanol in rodents. Thus, ethanol may increase ACh release into the VTA driving activation of DAergic neurons through nAChRs. In addition, ethanol potentiates distinct nAChR subtype responses to ACh and nicotine in vitro and in DAergic neurons. The smoking cessation therapeutic and nAChR partial agonist, varenicline, reduces alcohol consumption in heavy drinking smokers and rodent models of alcohol consumption. Finally, single nucleotide polymorphisms in nAChR subunit genes are associated with alcohol dependence phenotypes and smoking behaviors in human populations. Together, results from pre-clinical, clinical, and genetic studies indicate that nAChRs may have an inherent role in the abusive properties of ethanol, as well as in nicotine and alcohol co-dependence.

Clinical indices of familial alcohol use disorder

BACKGROUND

Alcohol use disorders (AUDs) are clinically heterogeneous and strongly influenced by familial/genetic factors. Can we identify specific clinical features of AUDs that index familial liability to illness?

METHODS

In twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders meeting DSM-IV criteria for lifetime AUDs, we examined whether clinical features of AUDs, including individual DSM-IV criteria for alcohol dependence (AD) and alcohol abuse (AA), predicted risk for AUDs in cotwins and/or parents. Analyses of individual criterion were repeated controlling for the total number of endorsed criteria.

RESULTS

Across these analyses, examining narrowly and broadly defined AUDs, risk of AUDs in relatives was more consistently predicted by abuse criteria than by dependence criteria, and by criteria reflecting negative psychosocial consequences rather than pharmacologic/biological criteria. Age at onset (AAO) poorly predicted risk in relatives. AUD associated legal problems, the one criterion slated for removal in DSM-5, was the most consistent single predictor of familial risk. Associations observed between individual criteria and risks of illness in relatives were generally stronger in monozygotic than dizygotic twin pairs, suggesting that these symptoms reflect a genetic risk for AUDs.

CONCLUSIONS

Individual DSM-IV criteria for AA and AD differ meaningfully in the degree to which they reflect the familial/genetic liability to AUDs. Contrary to expectation, the familial/genetic risk to AUDs was better reflected by symptoms of abuse and negative psychosocial consequences of AUD than by early AAO, or symptoms of tolerance and withdrawal.

Evidence for multiple genetic factors underlying the DSM-IV criteria for alcohol dependence

To determine the number of genetic factors underlying the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for alcohol dependence (AD), we conducted structural equation twin modeling for seven AD criteria, plus two summary screening questions, in 7133 personally interviewed male and female twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, who reported lifetime alcohol consumption. The best-fit twin model required three genetic and two unique environmental common factors, and criterion-specific unique environmental factors. The first genetic factor was defined by high loadings for the probe question about quantity and frequency of alcohol consumption, and tolerance criterion. The second genetic factor loaded strongly on the probe question about self-recognition of alcohol-related problems and AD criteria for loss of control, desire to quit, preoccupation and activities given up. The third genetic factor had high loadings for withdrawal and continued use despite the problems criteria. Genetic factor scores derived from these three factors differentially predicted patterns of comorbidity, educational status and other historical/clinical features of AD. The DSM-IV syndrome of AD does not reflect a single dimension of genetic liability, rather, these criteria reflect three underlying dimensions that index risk for: (i) tolerance and heavy use; (ii) loss of control with alcohol associated social dysfunction and (iii) withdrawal and continued use despite problems. While tentative and in need of replication, these results, consistent with the rodent literature, were validated by examining predictions of the genetic factor scores and have implications for gene-finding efforts in AD.

Offspring ADHD as a risk factor for parental marital problems: controls for genetic and environmental confounds

BACKGROUND

Previous studies have found that child attention-deficit/hyperactivity disorder (ADHD) is associated with more parental marital problems. However, the reasons for this association are unclear. The association might be due to genetic or environmental confounds that contribute to both marital problems and ADHD.

METHOD

Data were drawn from the Australian Twin Registry, including 1,296 individual twins, their spouses, and offspring. We studied adult twins who were discordant for offspring ADHD.Using a discordant twin pairs design, we examined the extent to which genetic and environmental confounds,as well as measured parental and offspring characteristics, explain the ADHD-marital problems association.

RESULTS

Offspring ADHD predicted parental divorce and marital conflict. The associations were also robust when comparing differentially exposed identical twins to control for unmeasured genetic and environmental factors, when controlling for measured maternal and paternal psychopathology,when restricting the sample based on timing of parental divorce and ADHD onset, and when controlling for other forms of offspring psychopathology. Each of these controls rules out alternative explanations for the association.

CONCLUSION

The results of the current study converge with those of prior research in suggesting that factors directly associated with offspring ADHD increase parental marital problems.

The genetics of alcohol dependence

Alcohol consumption dates back to the Neolithic period, and alcohol dependence contributes substantially to the current global burden of disease. Despite this, optimal therapies and preventive strategies are lacking. Formal genetic studies of alcohol dependence have shown that genetic factors play as large a role in disease etiology as environmental factors. Molecular genetic studies may identify causal factors and facilitate the development of novel preventive and therapeutic approaches. Whereas earlier studies involved the use of linkage- and candidate-gene approaches, recent years have witnessed the introduction of genome-wide association studies (GWAS). The present review provides a brief overview of the findings of formal genetic studies, summarizes the results of earlier molecular-genetic investigations, and presents a detailed overview of all published GWAS in the field of alcohol dependence research. To date, few genome-wide significant findings have been reported. However, through the polygenic approach, GWAS have both confirmed the existence of a multitude of novel risk genes and indicated interesting new candidates.